1. Field of the Invention
This invention relates to a semiconductor device having a metal layer formed on a semiconductor substrate, an opening penetrating through the semiconductor substrate to expose the metal layer and a wiring that is connected with the metal layer through the opening and its manufacturing method. Specifically this invention relates to a technology to monitor a result of the formation of the opening.
2. Description of the Related Art
A CSP (Chip Size Package) has received attention in recent years as a three-dimensional mounting technology as well as a new packaging technology. The CSP means a small package having about the same outside dimensions as those of a semiconductor die packaged in it.
A BGA (Ball Grid Array) type semiconductor device has been known as a kind of CSP. A plurality of ball-shaped conductive terminals made of metal such as solder is arrayed in a grid pattern on one principal surface of a package of the BGA type semiconductor device and is electrically connected with the semiconductor die mounted on the other side of the package. When the BGA type semiconductor device is mounted on electronic equipment, the semiconductor die is electrically connected with an external circuit on a printed circuit board by compression bonding of the conductive terminals to wiring patterns on the printed circuit board.
Such a BGA type semiconductor device has advantages in providing a large number of conductive terminals and in reducing size over other CSP type semiconductor devices such as an SOP (Small Outline Package) and a QFP (Quad Flat Package), which have lead pins protruding from their sides. The BGA type semiconductor device is used as an image sensor chip for a digital camera incorporated into a mobile telephone, for example. An example of the BGA type semiconductor device includes a supporting member made of a glass, for example, attached to one of, or both of principal surfaces of the semiconductor die. Further description on the technologies mentioned above is provided in Japanese Patent Application Publication No. 2003-309221, for example.
Next, a manufacturing method of the BGA type semiconductor device, that includes the supporting member attached to one of the principal surfaces of the semiconductor die, will be described referring to the drawings.
FIGS. 8 through 10 are cross-sectional views showing the manufacturing method of the BGA type semiconductor device, that is applicable to an image sensor chip, according to a conventional art.
First, a pad electrode 32, that is a metal layer primarily composed of aluminum, is formed on a front surface of a semiconductor substrate 30 through an insulation layer 31 made of a silicon oxide film or a silicon nitride film, as shown in FIG. 8. Then a supporting member 34 made of glass, for example, is bonded to the semiconductor substrate 30 having the pad electrode 32 through an adhesive material 33 made of an epoxy resin layer.
Next, a photoresist layer 35 having an opening at a location corresponding to the pad electrode 32 is formed on a back surface of the semiconductor substrate 30. Plasma-etching is performed on the semiconductor substrate 30 with etching gas composed of SF6 and O2, for example, using the photoresist layer 35 as a mask, and further etching is performed on the insulation layer 31 to form an opening 36 extending from the back surface of the semiconductor substrate 30 to the pad electrode 32, as shown in FIG. 9.
An insulation layer 45 made of a silicon oxide film, for example, is formed on the back surface of the semiconductor substrate 30 including the inside of the opening 36. After the insulation layer 45 on the pad electrode 32 is removed, a barrier layer 37 is formed on the entire surface, as shown in FIG. 10. A seed layer 38 for plating is formed on the barrier layer 37 and a wiring layer 39 made of copper (Cu), for example, is formed on the seed layer 38 by plating. After a protection layer 40 is formed on the wiring layer 39, openings are formed in predetermined locations in the protection layer 40 and conductive terminals 41, that make contact with the wiring layer 39, are formed in the openings.
Then, the semiconductor substrate 30 and the layers stacked on it are cut into individual semiconductor dice, although not shown in the figure. A BGA type semiconductor device, in which the pad electrode 32 and the conductive terminal 41 are electrically connected, is formed as described above.
However, the shape of the opening 36 that is actually formed can not be recognized after the opening 36 is completed as described above, unless the semiconductor wafer is cut and a cross-section of the cut wafer is observed. That is, since the opening 36 is formed from the back surface of the opaque semiconductor substrate 30 so as to expose the pad electrode formed on the front surface of the semiconductor substrate 30 through the insulation layer 31, it is necessary to observe the opening 36 from a transparent supporting member 34 side of the semiconductor substrate 30, when the observation of the opening 36 is to be made through a microscope. When observed from the direction of the supporting member 34, however, the opening 36 is not visible because of the existence of the pad electrode 32 that is the metal layer. Therefore, it is not possible to determined just by looking at the completed devices if the semiconductor substrate 30 is completely removed in the opening 36 or it is not as indicated by dashed lines in FIG. 11. In addition, the opening size at the bottom end of the opening 36 may become too large because of the over-etching. Also, it is not possible to measure an aperture of the opening 36 visually.